Conventionally, in shift switching mechanisms changing a shift position of an automatic transmission by electric control according to manipulation of a shift lever by a driver, those equipped with an electric motor (for example, a direct current motor) as a motive power source for switching the shift position have been known.
According to a shift switching mechanism as described above, there is no need to mechanically connect a shift lever with the shift switching mechanism as in a common switching mechanism that directly changes a shift position of an automatic transmission using a manipulation force applied to a shift lever by a driver. Therefore, there is no limitation in layout when these components are mounted in a vehicle, and thus the degree of freedom in design can be increased. Further, there has been an advantage that mounting to a vehicle can be easily performed.
As a shift switching mechanism as described above, for example, Japanese Patent Laying-Open No. 2005-69406 discloses a shift range switching device for an automatic transmission reducing a load on a shift switching mechanism applied when a shift position is switched. The shift range switching device for an automatic transmission includes shift means for rotating an actuator and changing a shift position to one of a plurality of shift positions, storage means for storing the shift position changed by the shift means, first restriction means for restricting rotation of the actuator in a predetermined direction in a first shift position of the plurality of shift positions, and control means for controlling the rotation of the actuator. The control means includes first location setting means for setting a location where the rotation of the actuator is stopped by the first restriction means as a first reference location in the first shift position, power supply control means for permitting cut-off of electric power supply to the shift range switching device in the first shift position, and reference location resetting means for resetting the first reference location by the first location setting means if the electric power supply is resumed after being cut off when the shift position stored by the storage means is uncertain.
According to the shift range switching device for an automatic transmission disclosed in the publication described above, deformation of a detent spring can be prevented or reduced by setting the reference location of the actuator based on a parking position. Since the deformation of the detent spring can be prevented or reduced, the shift switching mechanism has an improved durability. As a result, a load applied on the shift switching mechanism can be reduced.